With Eclipse 4.4.1 CDT and the in-tree Eclipse project builder (./mach build-backend -b CppEclipse), the Eclipse C++ tools work really well on Gecko. Features I really enjoy:

• Ctrl-click to navigate to definitions/declarations
• Ctrl-T to popup the superclasses/subclasses of a class, or the overridden/overriding implementations of a method
• Shift-ctrl-G to find all uses of a declaration (not 100% reliable, but almost always good enough)
• Instant coloring of syntax errors as you type (useless messages, but still worth having)
• Instant coloring of unknown identifier and type errors as you type; not 100% reliable, but good enough that most of my compiler errors are caught before doing a build.
• Really good autocomplete. E.g. given

  nsTArray> array;
  for (auto& v : array) {
    v->P

  Eclipse will autocomplete methods of Foo starting with P ... i.e., it handles "auto", C++ for-range loops, nsTArray and nsRefPtr operator overloading.
• Shift-ctrl-R: automated renaming of identifiers. Again, not 100% reliable but a massive time saver nonetheless.

Thanks to Jonathan Watt and Benoit Girard for the mach support and other Eclipse work over the years!

I assume other IDEs can do these things too, but if you're not using a tool at least this powerful, you might be leaving some productivity on the table.

With Eclipse, rr, and a unified hg repo, hacking Gecko has never felt so good :-).

http://robert.ocallahan.org/2015/03/eclipse-gecko-win.html